The UK's most complete GLP-1 guide
Every Question Answered. Every Side Effect Explained.
- How GLP-1 medications work
- Mounjaro vs Wegovy compared
- Injection instructions
- Side effects & solutions
- What to eat on treatment
- FAQs answered
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Weight Formula — UK Health Guidance
A weight formula is a mathematical calculation used to assess your health status and determine healthy weight ranges specific to your height. In the UK, the most commonly used formula is the Body Mass Index (BMI), which divides your weight in kilograms by your height in metres squared. Understanding these formulas helps you interpret NHS health guidance and track progress towards a healthier weight. Our free BMI calculator simplifies these calculations instantly, so you don't need to work them out manually.
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Calculate Your BMI Instantly
Enter your height and weight below. Supports both imperial (stone & lbs) and metric (kg). Results include NHS category, healthy weight range, and ethnicity adjustments.
What Is BMI and Why Does It Matter?
Body Mass Index (BMI) is the most widely used screening tool for assessing whether your weight falls within a healthy range. Used by the NHS, GPs, and weight management services across the UK, BMI provides a quick snapshot of your weight relative to your height. The formula is simple: your weight in kilograms divided by your height in metres squared (kg/m²).
While BMI isn't a perfect measure — it doesn't account for muscle mass, bone density, or fat distribution — it remains the standard first step in identifying potential weight-related health risks including type 2 diabetes, cardiovascular disease, high blood pressure, and certain cancers.
The NHS also recommends adjusted thresholds for people of South Asian, Chinese, or Black African heritage — a BMI of 23 or above is classified as overweight, and 27.5 as obese. Our calculator includes this adjustment as a one-click toggle.
Key Weight Formulas Used in UK Health Guidance
The BMI formula is the primary weight assessment tool recommended by the NHS. It's calculated as: weight (kg) ÷ height (m)². For example, if you weigh 70kg and are 1.75m tall, your BMI is 70 ÷ (1.75)² = 22.9, which falls in the healthy weight range. The NHS uses these BMI categories: underweight (below 18.5), healthy weight (18.5–24.9), overweight (25–29.9), obese class I (30–34.9), obese class II (35–39.9), and severely obese (40+). For adults of South Asian, Chinese, Black African, or Black Caribbean heritage, lower thresholds apply due to higher health risks at the same BMI. The healthy weight range formula calculates the weight you should aim for at your height: multiply 18.5 by your height in metres squared for the lower bound, and 24.9 for the upper bound. These formulas form the basis of NHS weight management guidance and help GPs assess your individual health.
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How It Works
Three simple steps to understand your weight and take action.
Enter your height and weight in our free calculator. Get your BMI, NHS category, healthy weight range, and ethnicity-adjusted thresholds instantly.
If your BMI suggests you're overweight or obese, explore our GLP-1 calculators to project potential weight loss on Mounjaro or Wegovy.
Use our progress tracker to log your weight weekly, visualise your journey with charts, and stay motivated — all stored privately in your browser.
Free Weight Loss Tools & Guides
Everything you need to understand your weight, explore medication options, and track your progress — completely free.
Using Weight Formulas with UK Health Resources
NHS guidance recommends using weight formulas alongside other health markers like waist circumference and blood pressure rather than relying on weight alone. The waist-to-height ratio is another useful formula: divide your waist circumference by your height (using the same units) — a ratio below 0.5 is considered healthy for all adults. You can also use weight conversion formulas to switch between imperial and metric measurements common in the UK: multiply kilograms by 2.20462 for pounds, or divide by 6.35029 for stone. Our free weight converter and BMI calculator handle these formulas automatically, giving you gradual improvement for NHS health assessments. Your GP can explain what these formulas mean for your individual health and whether lifestyle changes, weight management support, or further assessment might be beneficial.
- Dual GIP/GLP-1 receptor agonist
- Up to 22.5% body weight loss (SURMOUNT-1)
- Weekly injection, dose escalation over 20+ weeks
- Available via private prescription in the UK
- Doses: 2.5mg → 5mg → 7.5mg → 10mg → 12.5mg → 15mg
- GLP-1 receptor agonist
- Up to 15–17% body weight loss (STEP trials)
- Weekly injection, 5-step dose escalation
- NHS & private prescription available
- Doses: 0.25mg → 0.5mg → 1mg → 1.7mg → 2.4mg
Mounjaro vs Wegovy: Head-to-Head
A side-by-side comparison of the two most popular GLP-1 weight loss medications available in the UK.
| Feature | Mounjaro | Wegovy |
|---|---|---|
| Drug class | Dual GIP/GLP-1 agonist | GLP-1 agonist |
| Active ingredient | Tirzepatide | Semaglutide |
| Avg. weight loss | 15–22.5% | 12–17% |
| Key trial | SURMOUNT-1 (2022) | STEP 1 (2021) |
| Max dose | 15 mg weekly | 2.4 mg weekly |
| Escalation period | 20–32 weeks | 16–20 weeks |
| Administration | Weekly injection (pen) | Weekly injection (pen) |
| NHS availability | Private prescription only | NHS & private |
| Approx. private cost | £150–£250/month | £150–£300/month |
| Common side effects | Nausea, diarrhoea, constipation | Nausea, vomiting, diarrhoea |
Data sourced from SURMOUNT-1 and STEP 1 clinical trials. Costs are approximate and vary by provider. Always consult a prescriber.
Am I Eligible for Weight Loss Medication?
In the UK, eligibility for GLP-1 weight loss medications like Mounjaro and Wegovy is based on your BMI and overall health profile.
- BMI of 30 or above (obese)
- Age 18 or over
- No contraindicated conditions
- Committed to lifestyle changes
- BMI of 27 or above
- Plus type 2 diabetes
- Or high blood pressure
- Or obstructive sleep apnoea
Use our BMI calculator to check whether your BMI falls within the eligible range.
How We Built These Tools
Every calculator and guide on myweightcheck is built with accuracy and transparency in mind. Our BMI calculator uses the standard WHO formula with NHS-aligned category thresholds. Our GLP-1 projections are modelled on published clinical trial data from SURMOUNT and STEP studies.
All data stays on your device. We don't require sign-ups, and we don't store your health information on any server. Your progress tracker saves data locally in your browser using localStorage, so only you can see it.
We're based in the UK and our tools are designed specifically for UK users — supporting stone & lbs by default, referencing NHS guidelines, using NICE-approved medication data, and linking to GPhC-registered pharmacies.
Frequently Asked Questions
Common questions about BMI, weight loss medications, and our free UK tools.
What is the BMI weight formula used by the NHS?
The BMI formula is weight (kg) ÷ height (m)². The NHS uses this to categorise adults into healthy weight, overweight, or obese ranges. For example, 70kg at 1.75m height gives a BMI of 22.9, which is healthy. Use our free BMI calculator above to calculate yours instantly without a UK pharmacy maths.
How do I calculate my healthy weight range in UK measurements?
Multiply 18.5 by your height in metres squared for the lower bound, and 24.9 for the upper bound. For someone 1.73m tall, the healthy range is approximately 55–74kg (8st 10lbs to 11st 10lbs). Your GP can advise on whether you should aim towards this range based on your individual health.
What does the waist-to-height ratio formula measure?
The waist-to-height ratio divides your waist circumference by your height (in the same units). A ratio below 0.5 is healthy for all adults and indicates lower cardiovascular risk. This complements BMI as a health assessment tool, since BMI alone doesn't distinguish between muscle and fat mass.
How do I convert my weight between kg, stone, and pounds?
Divide kilograms by 6.35029 for stone, or multiply kilograms by 2.20462 for pounds. For example, 70kg equals 11 stone 0.1lbs. Our free weight converter above handles these formulas instantly — just enter your weight and switch between units.
Do weight formulas work the same for everyone in the UK?
Not entirely. The NHS recommends lower BMI thresholds (18.5–22.9 healthy range) for people of South Asian, Chinese, Black African, or Black Caribbean heritage because these groups face higher health risks at lower BMI levels. Your GP can explain whether standard or adjusted thresholds apply to you.
Ready to take control of your weight loss journey?
Start with a free BMI check, explore your GLP-1 options, or begin tracking your progress today. No sign-up. No cost. Just results.